package com.example.arithmeticleetcode.learnArithmetic.heap;

import com.example.arithmeticleetcode.learnArithmetic.hash.printer.BinaryTreeInfo;

import java.util.Comparator;

/**
 * @program: arithmetic-leetcode
 * @description: 二叉堆 二叉堆的逻辑结构就是一颗全完二叉树  也叫作完全二叉堆  底层使用数组实现即可   (最大堆)
 * @author: FangZhen
 * @create: 2020-11-02 14:16
 **/
public class BinaryHeap<E> extends AbstractHeap<E> implements BinaryTreeInfo {

    private E[] elements;

    private static final int DEFAULT_CAPACITY = 10;

    public BinaryHeap(E[] elements, Comparator<E> comparator) {
        super(comparator);

        if (elements == null || elements.length == 0) {
            this.elements = (E[]) new Object[DEFAULT_CAPACITY];
        } else {
            size = elements.length;
            int capacity = Math.max(elements.length, DEFAULT_CAPACITY);
            this.elements = (E[])new Object[capacity];
            for (int i = 0, len = elements.length; i < len; i++) {
                this.elements[i] = elements[i];
            }
            heapify();
        }
    }

    public BinaryHeap(E[] elements) {
        this(elements, null);
    }

    public BinaryHeap() {
        this(null, null);
    }

    public BinaryHeap(Comparator<E> comparator) {
        this(null, comparator);
    }




    @Override
    public void clear() {
        for (int i = 0, len = elements.length; i < len; i++) {
            elements[i] = null;
        }
        size = 0;
    }

    @Override
    public void add(E element) {
        elementNotNullCheck(element);
        ensureCapacity(size + 1);
        elements[size++] = element;
        siftUp(size - 1);

    }

    @Override
    public E get() {
        emptyCheck();
        return elements[0];
    }

    @Override
    public E remove() {
        emptyCheck();
        int lastIndex = --size;
        E root = elements[0];
        elements[0] = elements[lastIndex];
        elements[lastIndex] = null;
        siftDown(0);
        return root;
    }

    @Override
    public E replace(E element) {
        elementNotNullCheck(element);
        E root = null;
        if (size == 0) {
            elements[0] = element;
            size++;
        } else {
            root = elements[0];
            elements[0] = element;
            siftDown(0);
        }
        return root;
    }

    /**
     * 批量建堆
     */
    private void heapify() {
        //自上而下的上滤
//        for (int i = 0; i < size; i++) {
//            siftUp(i);
//        }

        //自下而上的下滤
        for (int i = (size >> 1) - 1; i >= 0; i--) {
            siftDown(i);
        }

    }

    /**
     * 让index上的元素上率 O(logN)
     *
     * @param index
     */
    private void siftUp(int index) {
        E e = elements[index];
        while (index > 0) {
            int pIndex = (index - 1) >> 1;
            E p = elements[pIndex];
            if (compare(e, p) <= 0) break;
            //将父元素存储在index位置
            elements[index] = p;
            //重新赋值index
            index = pIndex;
        }
        elements[index] = e;
    }

    /**
     * 让index上的元素上率 O(logN)
     *
     * @param index
     */
    private void siftDown(int index) {
        E element = elements[index];
        int half = size >> 1;
        //第一个叶子节点的索引 == 非叶子节点的数量
        //必须保证index位置为非叶子节点
        while (index < half) {
            //index的节点有2种情况
            // 1 只有左子节点
            // 2 同时有左右子节点

            //默认为左子节点的索引
            int childIndex = (index << 1) + 1;
            E child = elements[childIndex];

            //右子节点
            int rightIndex = childIndex + 1;

            //选出左右子节点最大的那个
            if (rightIndex < size && compare(elements[rightIndex], child) > 0) {
                child = elements[childIndex = rightIndex];
            }

            if (compare(element, child) >= 0) break;

            //将子节点存放到index位置
            elements[index] = child;
            index = childIndex;
        }
        elements[index] = element;
    }



    private void emptyCheck() {
        if (size == 0) {
            throw new IndexOutOfBoundsException("Heap is empty");
        }
    }

    private void ensureCapacity(int capacity) {
        int oldCapacity = elements.length;
        if (oldCapacity >= capacity) return;
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        E[] newElements = (E[]) new Object[newCapacity];
        for (int i = 0; i < size; i++) {
            newElements[i] = elements[i];
        }
        elements = newElements;
    }

    private void elementNotNullCheck(E element) {
        if (element == null) {
            throw new IllegalArgumentException("element must be not null");
        }
    }

    @Override
    public Object root() {
        return 0;
    }

    @Override
    public Object left(Object node) {
        int index = ((int)node << 1) + 1;
        return index >= size ? null : index;
    }

    @Override
    public Object right(Object node) {
        int index = ((int)node << 1) + 2;
        return index >= size ? null : index;
    }

    @Override
    public Object string(Object node) {
        return elements[(int)node];
    }
}
